Antifoggants and stabilizers for photographic silver halide emulsions



United. States Patent Fritz Del-sch and Millet R. De Angelus,Binghamton,

N.Y., assignors to General Aniline & Film Corporation, New York, N.Y., acorporation of Delaware No Drawing. Application August 15, 1958 SerialNo. 755,149

6 Claims. (CI. 96-66) The present invention relates to the use ofantifogging and stabilizing agents for photographic silver halideemulsions and, more particularly, to the use of bis(carboxy loweralkyl-2,3-)quinoxalinyl dithio ethers, their salts and esters for suchpurpose.

Iti s known that light-sensitive emulsions such as gelatin silver halideemulsions have a tendency to fog. Such fog may be caused in a number ofways as, for example, by excessive ripening of the emulsion, duringstorage of the film particularly at elevated temperatures and humidityor by prolonged development of the exposed emulsion.

A great numberof substances have been described in the literature asbeing effective in preventing an increase in fog through stabilizing orcontrolling the keeping qualities of light-sensitive silver halideemulsions. Although many of these compounds have the ability to reducefog tendencies and to improve stability, they are deficient in that theylower the sensitivity of the emulsions and in many cases reduce opticaland dye sensitivity.

We have now found that bis(carboxy lower alkyl-2,3-) quinoxalinyl dithioethers, their salts and esters are not only excellent stabilizers orantifogging agents for lightsensitive silver halide emulsions but, inaddition, they have the ability of performing this function withoutlowering the sensitivity of the emulsion with which they are associatedor without reducing the sensitivity of the emulsion to light of longerwave length attributable to the presence of sensitizing dyes.

The use of such compounds to inhibit fog and to stabilize silver halideemulsions, either by locating the same in the emulsion, in layersadjacent thereto or in processing baths for the emulsions, constitutesthe purposes and objects of the present invention.

The stabilizers the use of which is contemplated herein may berepresented by the following formula:

wherein R is hydrogen; an aliphatic radical such as alkyl, i.e., methyl,ethyl, propyl, butyl, amyl or the like; hydroxyalkyl, i.e.,hydroxymethyl, hydroxyethyl and the like; carboxyalkyl, i.e.,carboxymethyl, carboxyethyl and the like; aryl such as phenyl, toluyl,naphthyl, carboxyphenyl, sulfophenyl and the like; aralkyl such asbenzyl or a monovalent cation such as sodium, potassium, silver,ammonium or the like and n is a whole number of from 1 to 3. Examples ofcompounds within the ambit of such formula which we have found to beeffective are:

(l) 2,3-quinoxaline dithio acetic acid (2) The methyl, phenyl or ethylester of 2,3-quinoxaline dithio acetic acid (3) 2,3-quinoxaline dithiopropionic acid and its sodium and silver salts The above compounds areprepared by refluxing 2,3- quinoxaline dithiol with a bromo aliphaticacid such as bromoacetic acid, fi-bromop-ropionic acid orgammabromobutyric acid in the presence of an acid binding agent such assodium hydroxide, pyridine or the like. After cooling, the reactionmixture is acidified with a dilute acid and the solid which isprecipitated is recrystallized from ethanol.

The free acid thus produced may be converted to its salt by reactionwith a water soluble compound containing the desired cation such aspotassium carbonate, sodium carbonate, silver nitrate, ammoniumcarbonate or the like.

If the esters-are desired, they are produced in the conventional mannerby refluxing the free acid with the desired alcohol or phenol in thepresence of hydrochloric acid.

Beneficial effects and fog reduction are obtained when solutions of theaforementioned compounds are incorporated in the silver halide emulsionsas ripening finals or as coating finals. Ripening finals" are added during the ripening or the sensitivity increasing stage of the emulsionmaking process. Suchradditions may be made before,'during or after thedecomposition of the soluble silver salt such as silver nitrate by meansof soluble halides such as potassium bromide in the presence of acolloidal carrier such as gelatine, .PVA, solubilized casein or albumin.9

Coating finals are added to the emulsion just prior to coating on asuitable support such as glass, paper or film at a time when theemulsion has nearly obtained its maximum sensitivity. 7

When used as ripening finals, our antifoggants or stabilizers are bestemployed in a concentration of 1 to 25 mgs. per .6 mol of silver halideand when used as coating finals in a concentration of 10 to 300 mgs. per.6 mol of silver halide. The concentration used depends on the type ofemulsion involved and it is recommended that the optimum concentrationbe determined from case to case. In some instances, it is advantageousto apply the antifoggant in a layer adjacent to the silver. halideemulsion layer, i.e., in an undercoating or in an antiabrasiongelatinsurface coating. In other cases, they may be applied in one orall processing baths. I

The antifoggants may be used in various photographic emulsions, e.g.,non-sensitized, orthochromatic, panchromatic, X-ray emulsions, paperemulsions and color emulsions. They may be used alone or in combinationwith other antifoggants and stabilizers or in combination with sulfur,-reduction, -metal, and noble metal sensitizers or in combination withhydroxypolyethenoxy derivatives, i.e., those obtained by reactingethylene oxide with an alcohol, phenyl, amine or the like. (See U.S.P.1,970,578.)

The invention is further illustrated by the following examples but it isto be understood that the invention is not to be restricted thereto.

Example I exposed in a Type IIB Sensitometer and developed in adeveloper of the following composition:

The results of this procedure are tabulated as follows:

Relative Fog at 12 Oven Fog Quantity of Compound Used Speed Developat 6'Dement velopment 100 15 .30 400 mgs 100 15 17 The stabilizer used inthis example was prepared as follows: To a solution containing 9 gramsof sodium hydroxide in 175 milliliters of water were added 9.7 grams of2,3-quinoxaline dithiol. To this solution in a small volume of waterwere added 13.9 grams of bromoacetic acid. The reactants were allowed toreflux for 3 hours. The reaction mixture was then cooled and acidifiedwith concentrated hydrochloric acid to pH 2 and chilled in ice. Theprecipitate was collected, dissolved in ethanol, treated with charcoaland allowed to crystallize slowly overnight in a cooler.Recrystallization from ethanol gave 8 grams of a pure yellowishorangeproduct.

Example II The procedure was the same as in Example I excepting thatthere was used as the stabilizer 2,3-quinoxaline dithio propionic acid.The results were similar to those obtained in Example I.

The stabilizer was prepared in the same manner as that of Example Iwhile substituting p-bromopropionic acid for bromoacetic acid.

Example III Exposed samples of a photographic film were developed for 12minutes at 65 F. in a standard metol-hydroquinone developer. Two testswere made, one with a normal developing solution and one with adeveloper containing 500 mgs. of the stabilizer of Example I per oneliter of developer. Sensitometric strips developed in the normaldeveloper (control) for 12 minutes showed a fog of .30, whereas thosestrips which were developed in a developer containing the stabilizer hada fog of .20.

Example IV The procedure was the same as in Example III excepting thatthere was used as the stabilizer 2,3-quinoxaline dithio butyric acid.

The results were substantially the same as those of Example III.

The stabilizer of Example IV was prepared in the same way as that ofExample I while replacing the bromoacetic acid by gamma-bromobutyricacid.

Modifications of the invention will occur to persons skilled in the art.Thus, it is evident that in lieu of using the compounds of the examples,any of the compounds mentioned above may be employed with equally goodresults. We, therefore, do not intend to be limited in the patentgranted except as necessitated by the appended claims.

We claim:

1. A light-sensitive photographic material comprising a base and a lightsensitive silver halide emulsion layer thereon, said light-sensitivematerial containing as an antifoggant and stabilizer a compound of thefollowing formula:

wherein R is selected from the class consisting of hydrogen, analiphatic radical, aryl, aralkyl and a moncwalent cation, and n is awhole number from 1 to 3.

2. The article as defined in claim 1 wherein said antifoggant is locatedin the silver halide emulsion.

3. The article as defined in claim 1 wherein said antifoggant is locatedin a layer adjacent to said silver halide emulsion.

4. A light-sensitive photographic material comprising a base with alight-sensitive silver halide emulsion thereon, said emulsion containingas an antifoggant 2,3-quinoxaline dithio acetic acid.

5. The process of minimizing and preventing fog in light-sensitivesilver halide materials comprising a base having a light-sensitivesilver halide emulsion thereon which comprises exposing said emulsionand developing the same in a silver halide developer in the presence ofan antifoggant and stabilizer of the following formula:

References Cited in the file of this patent UNITED STATES PATENTS Allenet al. Apr. 24, 1956 Murray et al. Jan. 14, 1958

5. THE PROCESS OF MINIMIZING AND PREVENTING FOR IN LIGHT-SENSITIVESILVER HALIDE MATERIALS COMPRISING A BASE HAVING A LIGHT-SENSITIVESILVER HALIDE EMULSION THEREON WHICH COMPRISES EXPOSING SAID EMULSIONAND DEVELOPMENT THE SAME IN SILVER HALIDE DEVELOPER IN THE PRESENCE OFAN ANTIFOGGANT AND STABILIZER OF THE FOLLOWING FORMULA: